8/13/2019 Cheap Yagis

1/7

Cheap Yagi Antennas for VHF/UHF

by Kent Britain, WA5VJBedited by John Maca, AB5SS

[Editors notes:The antennas described in this article were built as the result of several discussions

between Kent and a Cuban radio operator. While there are plenty of high performance antenna designs,most of the parts required to build them are not available in Cuba. There just isn't an EPO or RadioShack available in Cuba. Kent accepted this as a challenge to design a really good antenna that couldbe built with little more than ground wire, coax and a wooden boom. Using the latest antenna designsoftware, he has developed several variations for 144 thru 1296 MHz. Apparently, the designs work verywell... Kent entered the 432 MHz version in a recent antenna contest and lost by 0.2 dB to a Midwestham who had copied his design. Though disappointed in losing, it did prove to Kent that the antennascan be easily replicated with consistant performance.]

If your planning to build an EME array, don't use these antennas. But, if you want to put together aRover station with less than $500 in the antennas or just want a good antenna for the home, read on.

These antennas are relatively small, easily constructed from common materials/tools and have surprisingperformance. The feed method is greatly simpified by directly soldering the coax to the driven element.No baluns or gamma matches are used in this design. This simplified feed uses the structure of theantenna itself for impedance matching. The spacing of the director and reflector elements from thedriven element directly affects the feed point impedance of the antenna. So, the design starts with thefeed (driven element) and the elements are built around it. Typically, a high gain antenna is designed inthe computer, then you try to come up with a matching arrangement for a 31.9 Ohm feed! For the costabout 0.5 dB of gain, these antennas make some design compromises for the feed impedance, use anasymmetrical feed and make trade offs for a very clean pattern. But, they allow simple measurements,have wide bandwidth, the ability to grow with the same element spacing AND... you can build theseantennas for $5!!!!

The booms used for these antennas is 1/2" X 3/4" wood. The elements have been made from siliconbronze welding rod, aluminum rod, hobby tubing and solid ground wire with no change in performance.Since you want to be able to solder to the driven element, silicon bronze welding rod, hobby tubing and#10 or #12 solid copper wire have been used and work fine. A drop of "Super Glue", epoxy or RTV isused to hold the elements in place. A good coat of Polyurethane should be applied to the wooden boomto protect it from the weather. A polyurethane varnished 902 MHz version has been in the air for a yearnow with little deterioration in performance.

And now for the antenna designs. These antennas have been carefully designed to have the highestdB's/Dollar ratio of anything around They were designed with YagiMax, tweaked using NEC and the

driven elements experimentally determined on the antenna range. The driven element design is the samefor all frequencies except for the length (L) and separation (H). See Figure 1 for details on the drivenelement. All dimensions are in inches.

8/13/2019 Cheap Yagis

2/7

8/13/2019 Cheap Yagis

3/7

8/13/2019 Cheap Yagis

4/7

144 MHz.This antenna is peaked for 144.2 MHz but performance is still good at 146.52 (emergencyuse only!) Driven element dimensions are L = 38.5" and H = 1.0" Elements are 1/8" diameter.

144 MHz REF DE D1 D2 D3 D4

3 ElementLengthSpacing

41.000.00

8.50

37.0020.00

4 Element

LengthSpacing

42.000.00

8.50

37.5019.25

33.0040.50

6 Element

LengthSpacking

40.500.00

7.50

37.5016.50

36.5034.00

36.5052.00

32.7570.00

8/13/2019 Cheap Yagis

5/7

8/13/2019 Cheap Yagis

6/7

8/13/2019 Cheap Yagis

7/7